Titanium dioxide (TiO2) is commercially produced by either the sulfate process or the chloride process. In the chloride process, titania-containing feedstocks are chlorinated to form titanium tetrachloride which is then oxidized to form TiO2. This process operates most efficiently starting from titania-containing feedstocks having high TiO2 content. Unfortunately, many titaniferous ores in their natural state, such as ilmenite, have TiO2 content in the range of 40% to 65% which is undesirably low for the chloride process.
Many different beneficiation methods for improving the TiO2 content of titaniferous ores have been developed. Slagging, for example, is utilized to upgrade ilmenite ores by reducing the majority of ferric and ferrous iron content to molten metallic iron in a furnace. The denser molten iron separates from the slag which floats on top of the molten iron phase. The slag contains a high percentage of TiO2 along with a lesser concentration of other impurities. The high percentage TiO2 slag with impurities is then separated from the molten iron and processed as a TiO2 feedstock.
Because the iron co-product from the slagging process can be sold as a feedstock for steel manufacture, slagging processes are economical for ilmenites having relatively low percentages of TiO2 concentrations.
However, since slagging processes are limited mostly to the separation of iron from the precursor ilmenite, significant levels of other impurities from the ilmenite feedstock can build up in the slag. Examples of such impurities are alkaline earth metals (e.g., Ca, Mg) and alkali metals (e.g., Na). Due to the high boiling points of the chloride compounds for these impurities, they can be harmful to the fluid bed chlorination process. As a result, a particular slag's impurities can relegate it to use with the less preferred sulfate process.
The Becher process is another process for upgrading ilmenite. Although the Becher process is a wet chemical process, its final product is similar to slag in that the Becher process removes iron while leaving all other non-ferrous impurities (calcium, alkali metals, etc.,) behind.
In addition to the ilmenite ores, there is an interest in developing processes from alternative ores containing relatively high levels of Is impurities that are not typically found in ilmenite. The removal and reclamation of some of these impurities could be commercially significant given the high price that some of these materials command. One such alternative ore is naturally occurring anatase TiO2 that is found in Brazil. This type of ore, as well as similar anatase ore bodies including blends of anatase and ilmenite, tend to have high levels of radionuclides, alkaline earth metals, rare earth metals, phosphates, and silica, which have limited their use due to the high costs of removing these impurities from the ore.
Acid leaching processes have been taught to remove iron oxide and other impurities from titaniferous ores. See, for example, U.S. Pat. Nos. 2,811,434, 3,777,013, 5,011,666, 5,085,837, 5,181,956, 5,826,162, and 6,048,505. Canadian Pat. No. 1,234,990 teaches a beneficiation process that comprises leaching ilmenite with a mineral acid, oxidizing and then reducing this intermediate concentrate, and then leaching the reduced intermediate to upgrade ilmenite.
There is a need to develop processes for removing impurities from ores, particularly those ores with high levels of non-ferrous impurities. The present invention provides such an improved process.